There is a need for exact, cost-effective microdosing systems in different fields, e.g. when dosing medicine or when dosing scents. Components of these microdosing systems are, normally, a fluid actuator, for example, a pump, e.g. a micromembrane pump and an element for monitoring the fluid flow, for example, a flow sensor.
Known microdosing systems, however, are usually large and expensive.
Micromembrane pumps having passive check valves are known, for example, from WO 03/095837 A1. The micromembrane pump disclosed therein is combined with a nozzle chip for generating a free jet disposed on the outlet side.
From WO 98/48330, for example, a flow sensor in the form of a microdosing chip is known that is based on the technology of a piezoresistive pressure sensor. The microdosing chip comprises a membrane. The membrane comprises an opening that serves as an orifice plate of a flow to be measured.
Piezoresistive pressure sensors are, on the one hand, cost-effective to produce, but, on the other hand, very sensitive against stress as induced in particular by the assembly, for example, by adhesing, clamping or the same. The microdosing chip known from the above stated WO 98/48330 shows the same behavior during assembly.
Due to such stress induced during assembly, known pressure and flow sensors, respectively, show undesired drift behavior when the same are assembled in a conventional manner. High-quality pressure and flow sensors, respectively, have to be assembled expensively in a stress-free manner for preventing the sensor drift, which, however, increases the costs.
Known options for reducing the sensor drift, are, for example, the adaptation of a glass wafer to the silicon wafer of the microdosing chip. Alternatively, the microdosing chip can be assembled in a very stress-free assembly method.
Such stress-free mounting methods, however, are very expensive, which again prevents the usage of such microdosing chips in applications necessitating low production costs.
If, however, microdosing pumps and microdosing chips are combined with one another in a cost-effective production method, the sensor value of the microdosing chip will drift due to the above stated reasons, i.e., due to the stress induced during assembly, which prevents exact dosing of the microdosing system.
Thus, there is a trade-off between a cost-effective production of a microdosing system where the pressure and flow sensor, respectively, still operate exactly, i.e., without any considerable drift.